It's the only thing that makes sense

 

Throughout the night there are noises that we simply sleep through.  As long as there is power coming to the house there will be noises from the furnace or air conditioning system.  Sounds come from the refrigerator, especially if it has an automatic ice maker.  There are hums and clunks that are not at all quiet.

There are wall clocks making noise and depending on the construction of your house, it will expand and contract as the outside temperature changes.  Should you put all these various sounds together, you’d have quite an orchestra tuning up, all while you are snoozing.

But let there be a single noise out of the ordinary, like a squeaky step, or a key being inserted into a lock and suddenly you’re wide awake.  Even the slightest pop or cracking noise and there you are, waiting to hear if there will be another or if it was something you imagined.

I believe this to be an exposed part of our survival mechanism.  Seldom used but always self-charging and ready to go.  It is just a part of us that doesn’t require a comb or make-up, but becomes more active if just before going to bed you watch a scary movie.